Lithium Cation Modification Markedly Enhances Ru Dispersion and CO<sub>2</sub> Methanation Activity on Ru/SiO<sub>2</sub> Catalysts
Shaorong Deng, Chen Zhu, Xiuzhong Fang, Xianglan Xu, Xiang Wang
Abstract
A series of Ru- x %Li + /SiO 2 catalysts ( x = 0.05–0.2), modified with varying amounts of lithium cation (Li + ), were prepared via coimpregnation and evaluated for CO 2 methanation to explore Li + modification on Ru/SiO 2 . Introducing trace Li + markedly boosts reaction activity, with the optimal Ru-0.1%Li + /SiO 2 exhibiting 38.4 and 12.3 times higher overall reaction rate and turnover frequency at 200 °C, respectively, compared to Ru/SiO 2 . Structural characterization confirmed that Li + incorporation effectively suppresses RuO 2 crystallization, thereby improving Ru dispersion from 9.1% to 31.5%, enhancing the active surface area from 33 to 115 m 2 g –1, while simultaneously reducing Ru particle size from 18.4 to 3.2 nm. In situ spectroscopy and surface reaction experiments revealed that the CO* pathway occurs for CO 2 methanation on both catalysts, which involves CO 2 dissociation and subsequent CO* hydrogenation. The smaller Ru nanoparticles on Ru-0.1%Li + /SiO 2 exhibit superior intrinsic activity for both steps compared to the larger nanoparticles on Ru/SiO 2 . The additional alkaline sites introduced by Li + additives also promote CO 2 dissociation. The exceptional activity of Ru-0.1%Li + /SiO 2 for CO 2 methanation is governed by the synergistic effect between the Ru particle size effect and Li + -induced basicity, with the former being predominant.